Diverse Microalgal Communities Maintain Robust and Resilient Nutrient Recovery across Variable Wastewater Influent Loadings and SRT

Microalgal biological nutrient recovery offers a promising solution for phosphorus (P) and nitrogen (N) recovery from wastewater, capable of meeting stringent effluent permit regulations (e.g., <0.04 mg·L^–1P) while producing valuable bioproducts such as biofuels and bioplastics. However, maintaining reliable long-term nutrient recovery and biomass productivity across variable environmental conditions and changing wastewater influent remains challenging as systems move toward full-scale implementation. This research investigated the impact of influent variable nutrient availability and influent perturbations across operational SRT to understand their effect on nutrient recovery and algal community dynamics. Laboratory-scale membrane photobioreactors (MPBRs) were operated under different SRTs (4, 8, and 12 days) with real secondary wastewater to examine the influence of N:P dynamics on intracellular N:P uptake and nutrient recovery, long-term system performance (>10 SRTs), and microbial community structure. The results show that influent nutrient variability strongly predicts nutrient recovery, with diverse microbial communities achieving high performance (95–100% P and N removal; <0.03 mg·L^–1effluent P) in periods of low nutrient variation across all SRTs and reactors. SRT was a strong driver of microalgae community structure and intracellular N:P. Diverse communities were correlated with high performance, and multiple genera (Chlorella, Desmodesmus, Koliella) were seen across SRTs, indicating high functional redundancy. Further, low SRT favored algae with fast growth and high nutrient uptake rates that limited perturbation effects (including nutrient variability and pest infection) and increased algal stability and resiliency despite lower biomass concentrations.